Mechanical loads opposing breathing elicit both physiological and perceptual responses. The purpose of the proposed studies is to apply detection threshold and magnitude estimation techniques to quantitatively investigate respiratory load perception in human subjects. The Stevens (power law) model will be utilized in the analysis of the magnitude estimation data. These psychophysical techniques will be used along with physiological methods to pursue the following objectives: 1) establish the quantitative relationship between load sensation and graded respiratory resistive (R) and elastic (E) loads in healthy subjects and determine the variability within and across subjects. 2) Determine the effect of background R and E loads on perception. This will be measured in two groups of subjects: a) healthy volunteers subjected to experimentally increased R and E background loads and b) patients with obstructive and restrictive pulmonary disease characterized by elevated intrinsic background R and E loads, respectively. 3) Assess the relative importance of the diaphragm in the perception of added loads. This objective will be pursued in two ways: a) studies of healthy subjects to examine the effect of altering the operating length-tension characteristics of the diaphragm (by abdominal compression) and, b) studies of patients with diaphragmatic paralysis but without lung disease. 4) Examine the potential interplay between respiratory load perception performance and respiratory control, particularly as related to responsiveness to added loads and chemical stimuli.